The major components of a gas turbine engine include (beginning at the upstream end, or inlet) a fan section, one or more compressor sections, a burner section, one or more turbine sections, and a nozzle. The engine may also include an afterburner.
Air enters the engine through the inlet, travels past the fan section, becomes compressed by the compressor sections, mixes with fuel, and combusts in the burner section. The gases from the burner section drive the turbine sections, then exit the engine through the nozzle. If present, the afterburner could augment the thrust of the engine by igniting additional fuel downstream of the burner section.
The conditions (e.g. temperature and stress) at which certain sections of an engine operate demand the use of high temperature and high strength materials. Such materials include nickel-based superalloys and titanium alloys. The cost of manufacturing parts made from these materials can be quite high. For example, certain engine parts made from these high temperature, high strength materials could have a value of approximately $200,000.
Errors can occur during the assembly or maintenance of the engine. Damage to parts can occur during the assembly, maintenance or operation of the engine. Such errors or damage create anomalies on the part that may render the part unsuitable for use. Due to the relatively high manufacturing costs of these parts, scrapping an unsuitable part is not preferred. Scrapping the unsuitable part should be used as a last resort since the engine part could have a value of over $200,000.
Rather, the preferred solution is to repair or to rework the unsuitable part. The repair/rework should remove the anomaly so as to render the part suitable for use. This obviously assumes that the part has suitable characteristics to withstand such repair or rework. However, current repair or rework techniques are not compatible with the aforementioned high temperature, high strength materials. Current techniques produce unwanted tensile debits and fatigue debits.
Current repair or rework techniques include fusion welding, plasma spraying, plating and brazing. Fusion welding unfortunately creates strain age cracking (particularly with the nickel-based superalloys) and embrittlement (particularly with the highly alloyed, alpha beta titanium materials) in these materials. Plasma spray and plating likewise create excessive residual stress in these materials due to the high thickness build-ups. Clearly, these techniques are not compatible with high temperature, high strength materials. Thus, a need exists for a repair or rework method that is compatible with the aforementioned high temperature, high strength materials.